This invention relates to a passenger seat and a passenger seat leg assembly which includes an energy-absorbing zone for providing controlled bending of the seat under bending stress. The invention is particularly adapted for application in connection with a machined, single piece leg assembly which includes diverging fore and aft legs and diverging fore and aft seat bottom supports. The legs are connected to a seating track in the floor and the seat bottom supports, together with other structure, support a seat bottom, including a seat cushion.
The seat disclosed in this application is intended for use in an aircraft passenger seat. Weight is a very significant factor in designing any structure for an aircraft. Weight relates directly to fuel consumption. For this reason every effort is made to design structures to be used in aircraft to be as light as possible consistent with other requirements. One of these other requirements is passenger safety. A seat could be built heavily and sturdily enough not be bend or break during an aircraft accident merely by fabricating it of heavy steel or of thick, solid aluminum. However, the weight penalty is so great that the use of such structures is economically impractical.
The prior art discloses the use of multiple-component seat frames fabricated of tubing bent into the proper shape and connected together by brackets. U.S. Pat. No. 4,718,719 discloses such a seat structure. Tubing is quite easy to bend, especially when already bent in the direction of expected further bending in case of extreme loading applied to the seat. Thus, the '719 Patent discloses the use of a curved plate which fits in the knee of the seat leg and spreads the loading along a greater portion of the length of the leg. See FIGS. 1 and 2 at 44 and 44', respectively.
Newer, unitary seat frames are not tubular but are solid metal with carefully positioned voids and areas of reduced thickness to decrease weight while maintaining adequate strength. Different problems are encountered with such seat frames, which are far more resistent to bending than tubular seat frames. Indeed, the unitary seat frames can be made so strong that substantially no bending occurs prior to actual breakage of the assembly. This is highly undesirable, since broken frame pieces could injure passengers, puncture or otherwise the degrade the integrity of fire-retardant barriers on the seats and impede passenger movement during and after an accident. In addition, the sudden breaking itself provides a rapid increase in g-forces which could also injure passengers.
FAA regulations provide limits within which seat frames must not permanently yield and higher limits within which the seat frames can yield but not fail. The seats must be made so that the fore seat bottom support and fore seat leg gradually collapse towards each other.
The prior art includes a unitary seat frame developed by applicant which includes a void in the area between the seat bottom support and leg intended to weaken the area sufficiently to provide a gradual bending and thus yielding of the leg and seat bottom support towards each other instead of sudden breaking.
This invention provides a means by which a unitary, or integrally-formed, seat frame can be constructed which maintains proper strength in the fore seat support and leg area. Gradual bending under stress is thereby maintained.